1. Field of the Invention
The present invention relates to a manufacturing method for microspheres (including emulsions and fine particles suspended in liquid) used in the food industry, the manufacturing of drugs and cosmetics, etc., and to an apparatus for carrying out the method.
2. Description of Related Art
Techniques in which a biphasic system, for which a separated state is thermodynamically stable, is formed, such as that composed of a water phase and an organic phase which are emulsified to obtain a semi-stable emulsion, are conventionally known. As general, well-known emulsification methods, there have been described in "Science of Emulsions" (Asakura-shoten, 1971), the methods of using a mixer, a colloid mill, a homogenizer, etc., and the method of dispersion with sound waves.
The general methods mentioned above have a disadvantage in that the diameters of dispersed phase particles in a continuous phase are distributed over a wide range.
Therefore, a method of using filtration by means of a membrane comprising polycarbonate (Biochemica et Biophysica Acta, 557 (1979), North Holland Biochemical Press); a method using repeated filtrations through a PTFE (polytetrafluoroethylene) membrane (Proceedings of the 26th Autumn Meeting of the Society of Chemical Engineers, Japan, 1993); and, a method of manufacturing homogenous emulsions by transferring a dispersed phase into a continuous phase through a porous glass membrane having uniform pores (Japanese Patent Application Laid-Open Nos. 2-95433, 5-220382 and 6-315617), have been proposed.
In addition, a method of manufacturing emulsions via fine pores formed in a membrane filter with a dry etching process or a wet etching process has been proposed in Japanese Patent Application Laid-Open No. 6-71150, a method of manufacturing emulsions by transferring a dispersed phase into a continuous phase through a nozzle has been proposed in Japanese Patent Application Laid-Open No. 60-5223, and a method of producing emulsions using a porous plate has been proposed in Japanese Patent Application Laid-Open No. 54-116389. In addition, a laminar-flow dripping method (KAGAKU KOOGAKU Vol. 21, No. 4, 1957) is also known.
Furthermore, a method of producing emulsions by transferring a dispersed phase into a continuous phase through microchannels having a predetermined width has been proposed (JAOCS, 74, 1997, pp. 317-321).
The method using filtration through a membrane comprising polycarbonate and the method using repeated filtrations through a PTFE membrane theoretically cannot manufacture emulsions comprising particles larger than the membrane pores and cannot separate particles smaller than the membrane pores. These methods are, therefore, especially unsuitable for producing emulsions comprising large particles.
In the method using a porous glass membrane having uniform pores, when the average diameter of the membrane pores is small, particle diameters are distributed in a narrow range and thus homogenous emulsions can be obtained. When the average diameter of the membrane pores is increased, however, particle diameters become distributed over a wide range so that homogenous emulsions cannot be obtained. In addition, in the laminar-flow dripping method using a nozzle or a porous plate, particle sizes become 1,000 .mu.m or more and are distributed over a wide range so that homogenous emulsions cannot be obtained.
In the method using microchannels having a predetermined width described in--JAOCS, 74, 1997, pp. 317-321--, homogenous emulsions can be obtained. However, as the method is a batch-type method, emulsions cannot be continuously produced. When the diameter of the channels is increased, the size of produced emulsions becomes large, and the emulsions cannot travel and unite with each other, so that homogenous emulsions cannot be obtained.
Therefore, the inventors of the present invention formerly proposed an apparatus which can continuously produce homogenous emulsions in International Publication No. W)97/30783.
The structure of this apparatus is shown in FIG. 14. In this apparatus for producing emulsions, a supply port 101 for a continuous phase (W) is formed in a side wall of a body 100, a supply port 103 for a dispersed phase (O) is formed in the center of a lid 102 which closes an upper opening of the body 100, and one or more withdrawal ports 104 for emulsions (E) are formed at a place apart from the center. A bulkhead member 106 formed between the lid 102 and a base 105 separates the supply port 103 for the dispersed phase (O) from the withdrawal ports 104 for emulsions (E). In addition, a supply port 107 for the dispersed phase (O) is formed in the center part of the base 105, a gap 109 is formed between the base 105 and a plate 108 placed opposite the base 105. In a boundary section 110 formed in the base 105 the dispersed phase (O) and the continuous phase (W) are separated, and, in a microchannel 111 formed in the boundary section 110, the dispersed phase (O) and the continuous phase (W) are mixed.
The dispersed phase (O) supplied to the inside of the bulkhead member 106 via the supply port 103 enters the gap 109 between the plate 108 and the base 105 via the supply port 107 and this dispersed phase (O) enters the continuous phase (W) through the boundary section 110, thereby forming emulsions.
With the above-mentioned apparatus, homogenous emulsions can be continuously obtained. However, it is necessary to supply power in order to withdraw emulsions and there is room for improvement with respect to the cost.